Ever since the advent of the first computer, there has been an unending drive to make computers and their components smaller, faster, and more powerful. These goals have created a whole new array of engineering concerns such as making a high number of robust electrical connections in very small spaces as well as providing for near-zero tolerance flatness of component casings. Other concerns include selecting materials to minimize differences in the coefficients of thermal expansion between the different types of conductive and non-conductive materials used in electronic components.
One type of computer-based electronic component is a land grid array (LGA) module which is an integrated circuit package that is connected to a printed circuit board via a land grid array (LGA) socket connector. A promising type of land grid array socket connector is an interposer which is disposed between the land grid array module and the printed circuit board. The interposer positions a contact array of the land grid array module in alignment with a contact array of the interposer, and positions a contact array of the printed circuit board in alignment with the contact array of the interposer. These aligned components are then compressed into a secured assembly of components to maintain electrical contact between respective elements of the contact arrays.
Various techniques have been employed to supply the compressive force on the component assembly, such as clamping with combinations of compressive screws, helical springs, and/or loading plates. A backing or stiffening plate is disposed on either side of the printed circuit board to lend additional support during application of the compressive force on the component assembly of the land grid array module, interposer, and printed circuit board. For example, see U.S. Pat. Nos. 6,549,418 and 6,198,630.
FIG. 1 illustrates a force pattern resulting from a conventional land grid array system that includes an array of conductive elements of a land grid array module in contact with an array of conductive elements of a printed circuit board via an interposer. As shown in FIG. 1, larger contact forces are observed near the corners and edges of the contact array with lesser contact forces observed near the center of the contact array. This force pattern is primarily the result of conventional securing mechanisms including helical springs mounted at the corners of these members which are used to create a compressive force between adjoining members. In addition, each contact element of in the array bears an individual load. While each contact element theoretically would bear the same force, in practice contact elements of the arrays near the center exhibit less force that contact elements of the arrays at the edges and corners. Moreover, even small variations in the flatness of various components, such as a land grid array module or a printed circuit board, as well as deflection of those components upon compression and electrical activation, contribute to variations in contact forces between adjacent contact elements of the arrays. Finally, not even the presence of a backing plate (or stiffening plate) can completely prevent or counteract deflections of the components (e.g. printed circuit board) that is caused by compressive loading.
Accordingly, despite constant refinement of compression techniques, the ongoing drive toward miniaturization and smaller tolerances places a continuing demand on improved compression techniques.